Method of producing electrical resistance heaters, and the improved heater products

ABSTRACT

This disclosure relates to a method of making an electrical heating unit comprising a concentric assembly of a helical wire electrical resistance heating element embedded in particulate insulating material and enclosed within an elongated sheath. The method comprises means for controlling the longitudinal expansion of the helix of the wire heating element and the uniformity of the helical pattern of the wire extending along the length of the heating unit. The disclosure also includes the improved products of the method which have more uniform heating capacities. This disclosure is especially advantageous and effective in continuous manufacturing systems for the formation and assembly of electrical heating units in extended uninterrupted lengths.

it 11 1 [11] 3,813,771 Sltoglantl June 4, 1974 [54} METHOD or PRODUCINGELECTRICAL RESISTANCE HEATERS, AND THE IMPROVED HEATER PRODUCTSInventor: Tholrbjorn Skogland, Shelbyville,

Assignee: General Electric Company,

Indianapolis, 1nd.

Filed: v July 2, 1973 Appl. No.: 376,103

US. Cl 29/615, 29/423, 29/611, 338/238, 338/267 llnt. Cl H0lc 15/04,H01c 17/00 Field of Search 29/615, 614, 613, 611, 29/423; 338/203, 238,267, 299

References Cited UNITED STATES PATENTS Desloge et al. 29/615 FOREIGNPATENTS OR APPLICATIONS 652,051 11/1962 Canada 29/614 PrimaryExaminer-Charles W. Lanham Assistant ExaminerV. A. DiPalma [57] ABSTRACTThis disclosure relates to a method of making an electrical heating unitcomprising a concentric assembly of a helical wire electrical resistanceheating element embedded in particulate insulating material and enclosedwithin an elongated sheath. The method comprises means for controllingthe longitudinal expansion of the helix of the wire heating element andthe uniformity of the helical pattern of the wire extending along thelength of the heating unit. The disclosure also includes the improvedproducts of the method which have more uniform heating capacities. Thisdisclosure is especially advantageous and effective in continuousmanufacturing systems for the formation and assembly of electricalheating units in extended uninterrupted lengths.

15 Claims, 4 Drawing Figures METHOD OF PRODUCKNG ELECTRllCAL RESISTANCEHEATERS, AND THE IMPROVED HEATER PRODUCTS BACKGROUND OF THE INVENTIONThe handling of typical helical or other sinuous shaped electricalresistance wire heating elements, and in particular their assemblywithin enclosed heater units, can be especially troublesome because ofthe typ ically very low resistance to longitudinal expansion and lack ofresiliency of the helical or sinuous configurations of high resistancematerials for such heating elements. This shortcoming of the heatingelement configuration and compositions is particularly evident wheninstalling a helical or sinuous resistance heating element within atube-like enclosing sheath, and also upon filling the interior of theenclosing sheath about the heating element with a particulate insulatingmaterial in the assembly of heater units. Moreover the very lowresistance to uncontrollable distension of the heating elementconfiguration renders it difficult to produce typical heating units withthe helical heating element contained within an elongated sheath andextended therein the length of the unit in a substantially uniformpattern or concentration, and in turn of uniform heat distributioncapabilities.

Prior efforts to overcome the difficulties of installing helical orsinuous electrical resistance wire heating elements in themanufacture'of typical heating units have resulted in complex and costlymeans and procedures,

for instance the use of periodic heater element supports in cooperationwith reduced portions in the sheath size such as advocated in US. Pat.No. 1,9l 1,063.

Moreover, the prior remedies such as proposed by US. Pat. No. 1,911,063,are not suitable or practical for use in continuous production systemsin the uninterrupted formation and assembly of typical heater units incontinuous lengths.

SUMMARY OF THE INVENTION This invention comprises a new method ofmanufacturing electrical heating units comprising a concentric assemblyof an electrical conducting resistance heating element or wire in theform ofa helix or other sinuous configuration, embedded in particulateinsulating material and enclosed within an elongated sheath, wherein thelongitudinal expansion of the helix or other sinuous configuration, andalso the uniformity of extension of the helix or other sinuous patternof the heating element within the heater product is controlled. Theinvention also includes the improved products of the method.

The invention comprises the application of a filament or thread-likestop member to regulate and restrain the lengthwise expansion of thehelix or sinuous configuration of the heating element during manufactureof the heating unit assembly. The restraining stop member is therafterdestroyed or effectively eliminated by the conventional swagingoperation which permit the helical or sinuous pattern of the element toextend itself substantially uniformly and approximately commenserate indegree with the elongation of the enclosing sheath or overall assemblyof the heating unit due to the swaging.

In the practice of this invention the filament-like stop member issecured to at least the leading end of the helical heating element whichis to be first introduced and passed into an enclosing sheath duringassembly. Thus, when moving the heating element within the confines ofthe sheath, the longitudinal expansion of its configuration can then becontrolled by restraining its extension to a substantially uniformexpansion of any predetermined or desired length by means of the stopmember.

Preferably the stop member is secured at several predetermined intervalsalong a considerable length of helical heating element with eachlocation of attachment defining a section of predetermined length.Alternatively, several individual stop members in sequence can besecured in series along the length of the helical heating element witheach individual member spanning a section of predetermined length.

Also predetermined lengths of individual sections of the helical heatingelement can be connected in continuous series through intermediateterminals, with the stop member or members spanning the length of eachsection of the heating element and secured to the intermediate terminalswhich join each section of the heating element.

The conventional swaging operation which is employed in the manufactureof this type of electrical heating unit to consolidate the granularinsulating material and product a reduction in the units cross-sectionwith a corresponding extension of its length, causes multiple breaksalong the length of the filamentary stop member. The breaking of thestop member releases the restraint upon the helical heating wire andpermits it to extend itself substantially uniformly and in an amountapproximately commensurate with the elongation of the enclosing sheath.The fractured remainants of the stop memberare not detrimental to theproduct in that they cause no discernable short circuiting or otherdegrading effects.

OBJECTS OF THE INVENTION A primary object of this invention is toprovide an effective method of controlling the degree and uniformity ofthe longitudinal'expansion of a helical or other sinuous electricalresistance heating element or wire in the manufacture of electricalheating units comprising a concentric assembly of a helical or sinuouselectrical heating element embedded in particulate insulating materialand enclosed within an elongated sheath.

Another object of this invention is to provide means for regulating thelongitudinal expansion of an electrical resistance heating elementhaving a helical or other sinuous configuration, and for regulating theuniformity of its extension throughout the performance of continuousmanufacturing processes for the production of extended uninterruptedlengths of electrical heating units comprising a concentric assembly ofan electrical resistance heating element embedded in particulateinsulating material and enclosed within an elongated sheath.

A further object of this invention is to produce improved electricalheating units having a heating elementor resistance wire therein ofhelical or other sinuous configuration which is extended in asubstantially uniform pattern and thereby provides uniform heating alongits length.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of asection of a consecutive series of helical electrical resistance heatingelements or wires joined together with intermediate connecting terminalmembers;

FIG. 2 is a partially sectionalized view of the section of the heatingelement ofFIG. 1, showing a preferred arrangement of the filamentarystop member which is suitable for use in a continuous manufacturingsystems, and the introduction of a leading end portion of the heatingelement into an enclosing sheath;

FIG. 3 is also a partially sectionalized view of the section andarrangement as in FIG. 2, showing the series of heating element and theintermediate connecting terminals members positioned generallyconcentrically within an enclosing sheath and embedded withinparticulate insulating material; and,

FIG. 4 shows a similar partially sectionalized view of the assembledproduct of FIG. 3 undergoing swaging whereby its cross-sectionaldiameter is reduced and its length extended, thereby causing multiplebreakes in the filamentary stop member.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawing whichillustratesa preferred embodiment of this invention, FIG. 1 shows aportion of a series of sinuous electrical resistance heating elementsfor the manufacture of electrical heating units, composed of alternatingunits ofa helical heating wire 12, 12', et seq., of any given lengthjoined together in series through intermediate sleeve-like terminalmembers 14, 14', et seq.

As shown in FIG. 2, one or more filamentary stop members 16, 16, etseq., and are affixed at 18, 18, et seq., such as by brazing orsoldering, to the interior of each intermediate terminal member I4, l4et seq.

The length ofa filamentary stop member 16, or a section thereof, ispredetermined in relation to the designed length for a section of thehelical configuration of the heating element 12. Thus the stop memberwill restrain or control the amount of longitudinal extension and theuniformity of the helix during the assembly of the heater unit whichincludes passing the helical heating wire into the elongated sheath 20,and the filling of the enclosing sheath with particulate insulatingmaterial about helix of the heating element contained therein. Thesubsequent swaging of the assembled unit breakes the stop member andreleases its restraining effect upon the helix thereby permitting thehelix to uniformly extend itself commensurate with the elongation of theassembled unit.

FIG. 2 shows a leading end portion 22 of electrical heating element 10being introduced and passed into a typical sheath member 20 inassemblying the unit. Introduction of a leading end portion andextension of the electrical heating element 10 within the sheath member20 may be effected by conventional means including pulling devices orsupporting frames (not shown). FIG. 3 shows the heating element 10positioned within the sheath 20 and the generally concentric arrangementof the assembly.

Particulate electrical insulating material 24 such as granular orpowdered metal oxides, for example magnesium oxide or aluminum oxide, orsilica, is introduced to substantially fill the space within sheath 20and about the helical wire 12, as shown in FIG. 3. The filling of thesheath and embedding of the electrical heating element with theinsulating granules serves to support and fix the position of the wirehelix in relation to the assembly as well as electrically insulate theelectrically conductive heating wire 12 from the surrounding sheath 20.

Following completion of the assembly, including introducing the helicalheating wire 12 into the enclosing sheath 20 and filling the sheath andembedding the helical wire in particulate insulating material, all whilercstraining the longitudinal expansion of the wire helix with the stopmember to any predetermined degree of extension and preserving theuniformity of its helical pattern, the assembly is subjected to aswaging operaton. Swaging is commonly achieved by passing the elongatedsheath and its assembled contents of resistance wire and particulateinsulation through two or more size reducing rolls 26, 26 whichprogressively reduces the cross-sectional dimension of the assemblywhile extending its length, thereby consolidating and compressing theparticulate insulating filler about the heating wire helix. The swagingof the assembly and its reduction in section and extension in length isillustrated in FIG. 4. The progression of the elongation or stretchingalong the length of the assembly due to the swaging produces aprogressive multiple breaking of the filamentary stop member along itslength such as shown in FIG. 4. This progressive sequential breaking ofthe stop member 16 releases its restraining effects in response to theelongation of the assemblage, and thereby enables the helicalconfiguration of the heating wire to be extended substantially uniformlyin length commensurate with the elongation of the enclosing sheath andits contents.

According to one embodiment ofthis invention, after completion of thesteps of assembly, a continuous unit or long section thereof can bedivided into several discrete units by cutting and separating theassembly at the predetermined locations of the intermediate terminalmembers 14, such as at broken lines CC in FIG. 4

This invention is especially useful in the manufacture of electricalheating units by means of continuous forming procedures wherein theenclosing sheath of the unit is progressively shaped from a strip ofmetal and the electrical resistance heating element and particulateinsulating material are continuously introduced into the formed sheath.Such continuous manufacturing procedures for the production ofelectrical heating units in continuous sections of very long lengths areknown in the prior art, such as shown in U.S. Pat. Nos. 1,127,281;1,192,457; 2,808,492; and French Pat. No. 902,739.

It should be appreciated that the advantages provided by this inventioncan also be beneficial in the manufacture of conventional heating unitsin individual sections of relatively short length, such as of only a fewfeet. For instance the steps of this invention apply and are effectivein substantially all systems of manufacture comprising passing a sinuousheating element into an enclosing sheath or tube and embedding it withinparticulate insulating material wherein any pulling or dragging forceupon the sinuous member may tend to over extend or nonuniformly expandit.

Moreover, it should be understood that in its broader aspects thisinvention includes affixing the filamentary stop member to a portion ofthe leading end of a length of sinuous heating element to be firstintroduced into a sheath, and restraining the elongation of the sinuousconfiguration of the element with the stop member to whatever degree orrelative rate of its extension is desired during its introduction into asheath, the thereafter filling of the sheath with insulating materialand compacting the same.

Although the invention has been described with reference to a preferredembodiment thereof, numerous modifications are possible and it isdesired to cover all modifications falling within the spirit and scopeof the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A method of making an electrical heating unit comprising a concentricassembly of a sinuous wire electrical resistance heating elementembedded in particulate insulating material and enclosed within anelongated sheath, comprising the steps of:

a. affixing a filamentary stop member to one end of a length of heatingelement having a sinuous configuration;

b. introducing the end of the heating element with the affixed stopmember into an elongated sheath and extending the heating element withthe stop member within the sheath while restraining the longitudinalexpansion of the sinuous configuration of the element with the stopmember;

c. substantially filling the elongated sheath with particulateinsulating material and embedding said sinuous heating element thereinwhile restaining the longitudinal expansion of the sinuous configurationof the element with the stop member; and,

d. swaging the resultant assembly of sinuous heating element embedded inthe particulate insulating material and enclosed within the elongatedsheath whereby the cross-section of the assembly is reduced and itslength is extended, and thereby breaking the filamentary stop member andpermitting thesubstantially uniform extension of the sinuousconfiguration of the heating element by an amount approximatelycommensurate with the elongation of the enclosing sheath.

2. A method of making an electrical heating unit comprising a concentricassembly ofa helical wire electrical resistance heating element embeddedin particu late insulating material and enclosed within an elongatedsheath, comprising the steps of:

a. affixing each end of a predetermined length of a filament stop memberto corresponding ends of a predetermined length of a helical heatingelement.

. swaging the resultant assembly of helical heating element embedded inthe particulate insulating material and enclosed within the elongatedsheath whereby the cross-section of the assembly is reduced and itslength is extended. and thereby breaking the filamentary stop member andpermit- 6 ting the substantially uniform extension of the helicalheating element approximately commensurate with the elongation of theenclosing sheath.

3. The method of making an electrical heating unit of claim 2, whereinthe filamentary stop member is affixed to the helical heating element atmultiple intervals of predetermined length.

4. The method of making an electrical heating unit of claim 3, whereinthe helical heating element comprises a series of discrete sections ofpredetermined length consecutively joined together by intermediateterminal members.

5. The method of making an electrical heating unit of claim 4, whereinthe filamentary stop member is affixed to the intermediate terminalmembers connecting the predetermined lengths of the helical heatingelement.

6. The method of making an electrical unit of claim 2, wherein a seriesof discrete filamentary stop members in predetermined lengths areconsecutively affixed at their ends to the helical heating element atintervals of predetermined length.

7. The method making an electrical heating unit of claim 6, wherein thehelical heating element comprises a series of discrete sections ofpredetermined length consecutively joined together by intermediateterminal members.

8. The method of making an electrical heating unit of claim 7, whereinthe ends of the discrete filamentary stop membersare affixed to theintermediate terminal members connecting the predetermined lengths ofthe helical heating element.

9. The method of making an electrical heating unit of claim 8, whereinthe elongated sheath iscontinuously formed by progressive shaping from astrip of metal, and the helical heating element with affixed stop memberand the particulate insulating material are continuously applied intothe continuously formed sheath.

10. A method of making an electrical heating unit comprising aconcentric assembly of a helical wire electrical resistance heatingelement embedded in particulate insulating material and enclosed withinelongated sheath, comprising the steps of:

a. continuously forming an elongated sheath;

b. affixing the ends ofa predetermined, length ofa filamentary stopmember to a helical heating wire at locations thereon defining apredetermined length;

c. continuously passing the helical heating wire with the affixed stopmember into the elongated sheath and substantially filling the elongatedsheath with particulate insulating material and embedding said helicalheating wire enclosed therein while restaining longitudinal expansion ofthe helix of the wire with the stop member; and,

d. continuously swaging the resulting assembly of helical heating wireembedded in the particulate insulating material and enclosed within theelongated sheath whereby the cross-section of the assembly is reducedand its length is extended, and thereby breaking the filamentary stopmember and permitting the substantially uniform extension of the helixof the wire by an amount approximately commensurate with the elongationof the enclosing sheath.

11. The continuous method of making an electrical heating unit of claim10, wherein the filamentary stop member is affixed to the helicalheating wire at a plurality of intervals of predetermined length.

member comprises a series of discrete filamentary stop members inpredetermined lengths with each consecutively affixed at its ends to aintermediate terminal member connecting the predetermined lengths of thehelical heating wire.

15. An electrical heating unit comprising a concentric assembly of asinuous wire electrical resistance heating element embedded inparticulate insulating material and enclosed within an elongated sheath,consisting of the product of claim 1.

1. A method of making an electrical heating unit comprising a concentricassembly of a sinuous wire electrical resistance heating elementembedded in particulate insulating material and enclosed within anelongated sheath, comprising the steps of: a. affixing a filamentarystop member to one end of a length of heating element having a sinuousconfiguration; b. introducing the end of the heating element with theaffixed stop member into an elongated sheath and extending the heatingelement with the stop member within the sheath while restraining thelongitudinal expansion of the sinuous configuration of the element withthe stop member; c. substantially filling the elongated sheath withparticulate insulating material and embedding said sinuous heatingelement therein while restaining the longitudinal expansion of thesinuOus configuration of the element with the stop member; and, d.swaging the resultant assembly of sinuous heating element embedded inthe particulate insulating material and enclosed within the elongatedsheath whereby the cross-section of the assembly is reduced and itslength is extended, and thereby breaking the filamentary stop member andpermitting the substantially uniform extension of the sinuousconfiguration of the heating element by an amount approximatelycommensurate with the elongation of the enclosing sheath.
 2. A method ofmaking an electrical heating unit comprising a concentric assembly of ahelical wire electrical resistance heating element embedded inparticulate insulating material and enclosed within an elongated sheath,comprising the steps of: a. affixing each end of a predetermined lengthof a filament stop member to corresponding ends of a predeterminedlength of a helical heating element. b. passing the predetermined lengthof the helical heating element with the affixed stop member into anelongated sheath, and substantially filling the elongated sheath withparticulate insulating material and embedding the said helical wiretherein while restraining the longitudinal expansion of the helicalheating element with the stop member; and, c. swaging the resultantassembly of helical heating element embedded in the particulateinsulating material and enclosed within the elongated sheath whereby thecross-section of the assembly is reduced and its length is extended, andthereby breaking the filamentary stop member and permitting thesubstantially uniform extension of the helical heating elementapproximately commensurate with the elongation of the enclosing sheath.3. The method of making an electrical heating unit of claim 2, whereinthe filamentary stop member is affixed to the helical heating element atmultiple intervals of predetermined length.
 4. The method of making anelectrical heating unit of claim 3, wherein the helical heating elementcomprises a series of discrete sections of predetermined lengthconsecutively joined together by intermediate terminal members.
 5. Themethod of making an electrical heating unit of claim 4, wherein thefilamentary stop member is affixed to the intermediate terminal membersconnecting the predetermined lengths of the helical heating element. 6.The method of making an electrical unit of claim 2, wherein a series ofdiscrete filamentary stop members in predetermined lengths areconsecutively affixed at their ends to the helical heating element atintervals of predetermined length.
 7. The method making an electricalheating unit of claim 6, wherein the helical heating element comprises aseries of discrete sections of predetermined length consecutively joinedtogether by intermediate terminal members.
 8. The method of making anelectrical heating unit of claim 7, wherein the ends of the discretefilamentary stop members are affixed to the intermediate terminalmembers connecting the predetermined lengths of the helical heatingelement.
 9. The method of making an electrical heating unit of claim 8,wherein the elongated sheath is continuously formed by progressiveshaping from a strip of metal, and the helical heating element withaffixed stop member and the particulate insulating material arecontinuously applied into the continuously formed sheath.
 10. A methodof making an electrical heating unit comprising a concentric assembly ofa helical wire electrical resistance heating element embedded inparticulate insulating material and enclosed within elongated sheath,comprising the steps of: a. continuously forming an elongated sheath; b.affixing the ends of a predetermined length of a filamentary stop memberto a helical heating wire at locations thereon defining a predeterminedlength; c. continuously passing the helical heating wire with theaffixed stop member into the elongated sheath and substantially fillingthe elongated sheath with particulate insulatiNg material and embeddingsaid helical heating wire enclosed therein while restaining longitudinalexpansion of the helix of the wire with the stop member; and, d.continuously swaging the resulting assembly of helical heating wireembedded in the particulate insulating material and enclosed within theelongated sheath whereby the cross-section of the assembly is reducedand its length is extended, and thereby breaking the filamentary stopmember and permitting the substantially uniform extension of the helixof the wire by an amount approximately commensurate with the elongationof the enclosing sheath.
 11. The continuous method of making anelectrical heating unit of claim 10, wherein the filamentary stop memberis affixed to the helical heating wire at a plurality of intervals ofpredetermined length.
 12. The continuous method of making an electricalheating unit of claim 11, wherein the helical heating wire comprises aseries of discrete sections of predetermined length consecutively joinedtogether by intermediate terminal members.
 13. The continuous method ofmaking an electrical heating unit of claim 12, wherein the filamentarystop member is affixed to the intermediate terminal members connectingthe predetermined lengths of the helical wire.
 14. The continuous methodof making an electrical heating unit of claim 13, wherein thefilamentary stop member comprises a series of discrete filamentary stopmembers in predetermined lengths with each consecutively affixed at itsends to a intermediate terminal member connecting the predeterminedlengths of the helical heating wire.
 15. An electrical heating unitcomprising a concentric assembly of a sinuous wire electrical resistanceheating element embedded in particulate insulating material and enclosedwithin an elongated sheath, consisting of the product of claim 1.